1. Field of the Invention
The present invention relates to a tire vulcanizer for squeezing upper molds and lower molds so as to vulcanize and pattern green tires, and a tire vulcanizing method.
2. Description of the Related Art
In a manufacturing step of a tire, a green tire made by assembling constituent members of the tire is vulcanized by a tire vulcanizer. A bladder to be inflated by a low-pressure pressure medium is closely attached to an inner circumferential surface of the green tire installed between openable and closable upper and lower molds by a center mechanism of the tire vulcanizer. After that, the green tire is heated from inside by squeezing of the upper and lower molds and introduction of a high-pressure heating medium to an interior of the bladder. The upper and lower molds are always heated by platen, the green tire is vulcanized by heating from an inner surface and an outer surface thereof.
There are various types of tire vulcanizers used in a vulcanization step. Japanese Unexamined Patent Application Publication No. H9-239734 discloses a twin type tire vulcanizer in which one open/close device opens and closes two sets of upper and lower molds. It should be noted that although a single type tire vulcanizer in which one open/close device opens and closes one set of upper and lower molds is used in the market, cost per one set of upper and lower molds is lower in the twin type tire vulcanizer. Thus, a use ratio of the twin type tire vulcanizer is extremely high.
Japanese Unexamined Patent Application Publication No. 2008-162269 discloses a tire vulcanizer in which pressure and a temperature of a heating and pressurizing medium supplied to an interior of a bladder are respectively individually controlled. This tire vulcanizer has a gas supply source for supplying a high-pressure nitrogen gas, and a gas supply source for supplying a low-pressure nitrogen gas. By supplying the low-pressure nitrogen gas to the interior of the bladder before vulcanization, the bladder is closely attached to an inner circumferential surface of a tire. At this time, the high-pressure nitrogen gas is preliminarily heated by a heating means while being circulated in a closed-loop medium circulating passage, and a medium supplying passage and a medium returning passage providing communication between the medium circulating passage and the interior of the bladder are closed by a valve operation.
A temperature of the high-pressure nitrogen gas circulated in the medium circulating passage is increased to a predetermined temperature. In this state, when upper and lower molds are closed and a squeezing force is imposed between the upper and lower molds, communication between the medium circulating passage, and the medium supplying passage and the medium returning passage is provided by the valve operation, so that the vulcanization is performed. The preliminarily heated high-pressure nitrogen gas is supplied to the interior of the bladder through the medium supplying passage. The nitrogen gas discharged from the interior of the bladder is recovered to the medium circulating passage through the medium returning passage.
In the tire vulcanizer of Japanese Unexamined Patent Application Publication No. 2008-162269, one system for circulating a heating and pressurizing medium with respect to one set of upper and lower molds is provided. However, as in Japanese Unexamined Patent Application Publication No. H9-239734, a twin type tire vulcanizer in which two sets of upper and lower molds are driven by one open/close device is widely used. When the system of Japanese Unexamined Patent Application Publication No. 2008-162269 is applied to the twin type tire vulcanizer, systems for circulating a heating and pressurizing medium are respectively provided for the two sets of upper and lower molds. In general, in the twin type tire vulcanizer, the tires of the same size are respectively vulcanized in the two sets of upper and lower molds. Therefore, the two same systems are uneconomically provided.